For mobile communication systems such as GSM, in each cell is allocated a group of frequency resources, and in adjacent cells are assigned frequency resource groups which are completely different from those of the neighbouring cells. The base station antenna of a cell is designed to achieve desired coverage within this particular cell. By limiting the boundaries of the coverage area within one cell, the same group of frequency resources can be used by other cells that are sufficiently separated from one another to keep the interference level within pre-defined limits. The design process of selecting and allocating frequency resources to cells within the desired coverage area is called frequency reuse (or frequency planning).
Currently, several schemes of frequency reuse such as semi-static and fractional frequency reuse are proposed for the Long Term Evolution of UMTS. The main idea is to divide whole frequency resources into several different sub-carrier groups. The cell centre users of every cell use the same sub-carrier group whereas the cell edge users use approximately orthogonal sub-carrier groups. Hence, different frequency reuse factors can be generated according to the user's location. The Signal to Interference Ratio of the cell edge users is increased while the spectral efficiency and data rate discrepancies between cell edge and cell centre users are minimized.
The semi-static frequency reuse scheme takes the traffic load at the cell edge into account. However, the allocation of the frequency resource requires a centralized scheduler. In the fractional frequency reuse scheme, a user can be treated as a cell edge or a cell centre user depending on its CQI feedback. Moreover, the proposed frequency reuse schemes, such as semi-static or fractional frequency reuse schemes, focus on the data channel, for which it is possible to make use of feedback to control the allocation of subcarriers.